The recombinant expression of therapeutic proteins in cell culture (particularly large-scale cell cultures), including eukaryotic cell culture, and more specifically mammalian cell culture, requires the use of special culture media providing nutrient substances for efficient growth of cells. Cell culture media formulations are often supplemented with a range of additives, including fetal calf serum (FCS), animal derived proteins and/or protein hydrolysates of bovine origin as well as protein hydrolysates derived from plants or yeast. One challenge with such cultures is that the amount of protein and the total and specific activity of the protein produced are often variable across different cell cultures, even when the formulation for the cell culture media is not changed. This variability is especially apparent in the case of large-scale manufacturing processes utilizing cell culture volumes of 10 liters to over 20,000 liters. Cell culture media containing hydrolysates are particularly prone to variability from one cell culture to the next, leading to decreased production of total protein as well as decreased total and specific activity.
One potential reason for the variability seen across different cell cultures is that contaminants in additives such as hydrolysates vary from one batch to the next. In general, serum or serum-derived substances, such as, e.g., albumin, transferrin or insulin, may comprise unwanted agents that can contaminate the cell cultures and the biological products obtained thereof. Furthermore, human serum derived additives have to be tested for all known viruses, including hepatitis viruses and HIV which can be transmitted via serum. Moreover, bovine serum and products derived thereof bear the risk of BSE contamination. In addition, all serum-derived products can be contaminated by unknown substances. When using serum or protein additives derived from human or animal sources in cell culture, there are numerous problems (e.g., the varying quality in composition of different batches and the risk of contamination with mycoplasma, viruses or BSE), particularly if the cells are used in the manufacture of drugs or vaccines for human administration. Therefore, many attempts have been made to provide efficient host systems and cultivation conditions, which do not require serum or other animal protein compounds.
Such serum-free media have been developed on the basis of protein extracts derived from plants or yeast. For example, soy hydrolysates are known to be useful for fermentation processes and can enhance the growth of many fastidious organisms, yeasts and fungi. WO 96/26266 describes that papaic digests of soy meal are a source of carbohydrate and nitrogen and many of the components can be used in tissue culture. Franek et al. (Biotechnology Progress (2000) 16, 688-692) describe growth and productivity promoting effects of defined soy and wheat hydrolysate peptide fractions.
WO 96/15231 discloses a serum-free medium composed of a synthetic minimal essential medium and a yeast extract for the propagation of vertebrate cells and a virus production process. A medium formulation composed of a basal cell culture medium comprising a rice peptide and an extract of yeast and an enzymatic digest thereof, and/or a plant lipid for growth of animal cells is disclosed in WO 98/15614. A medium comprising purified soy hydrolysate for the cultivation of recombinant cells is disclosed in WO 01/23527. WO 00/03000 discloses a medium that comprises a soy hydrolysate and a yeast extract, but also requires the presence of recombinant forms of animal proteins, such as growth factors.
EP-A-0 481 791 describes a biochemically defined culture medium for culturing engineered CHO cells, which is free from protein, lipid and carbohydrate isolated from an animal source, further comprising a recombinant insulin or insulin analogue, 1% to 0.025% w/v papain digested soy peptone and putrescine. WO 98/08934 describes a serum-free eukaryotic cell culture comprising hydrolyzed soy peptides (1-1000 mg/L), 0.01 to 1 mg/L putrescine and a variety of animal-derived components, including albumin, fetuin, various hormones and other proteins. In this context, it should be noted that putrescine is also known to be comprised in standard media like DMEM/Ham's F12 in a concentration of 0.08 mg/L.
The plant and/or yeast hydrolysates, however, are undefined mixtures of oligopeptides and other unknown components and contaminants. Moreover, the quality of commercially available lots of hydrolysates varies extremely. As a result, there are large variations in the production of recombinant proteins or viral products (a variation of up to a factor of three) as a function of the lots of hydrolysates used (“lot-to-lot variation”). This drawback affects the proliferation of the cells as well as the protein expression of each cell. US 2007/0212770 describes various animal protein-free and oligopeptide-free, chemically defined culture mediums that are useful for the large-scale production of recombinant protein biopharmaceuticals.
Hemostasis involves the interaction of various hemostatic reaction routes finally leading to thrombus formation. Thrombi are deposits of blood components on the surface of the vascular wall that mainly consist of aggregated blood platelets and insoluble cross-linked fibrin. Fibrin formation is the result of the restricted proteolysis of fibrinogen by thrombin, a coagulation enzyme. Thrombin is the end product of the coagulation cascade, a succession of zymogen activations occurring on the surfaces of activated blood platelets and leucocytes, and a variety of vascular cells (for a survey, cf. K. G. Mann et al., Blood, 1990, Vol. 76, pp. 1-16).
An important function in the coagulation cascade resides in the activation of Factor X by the complex of activated Factor IX (Factor IXa) and activated Factor VIII (Factor VIIIa). A deficiency or a dysfunction of the components of this complex is associated with the blood disease known as hemophilia (J. E. Sadler & E. W. Davie: Hemophilia A, Hemophilia B, and von Willebrand's Disease, in G. Stamatoyannopoulos et al., (Eds.): The molecular basis of blood diseases. W.B. Saunders Co., Philadelphia, 1987, pp. 576-602). Hemophilia A is related to a deficiency of Factor VIII activity, whereas Hemophilia B is related to a Factor IX deficiency. Current treatment consists of a replacement therapy using pharmaceutical preparations comprised of the normal coagulation factor. Of these thrombopathies, Hemophilia A occurs more frequently, affecting approximately one out of 10,000 men. Replacement therapy in Hemophilia A patients involves the repeated administration of preparations containing normal Factor VIII by intravenous infusion. The interval between the infusions is a function of the degradation of the Factor VIII activity in blood circulation. The half-life of the Factor VIII activity after an infusion differs from one individual to another, ranging from 10 to 30 hours. Thus, a prophylactic therapy requires an infusion every two to three days. This constitutes a heavy load on the life of hemophilic patients, in particular, if the venous access has become difficult due to local citratization following frequent needle punctures for intravenous infusions.
It would be particularly advantageous if the frequency of infusions could be lowered by using Factor VIII having extended half-lives. It is well known in the art that the half-life of the non-activated Factor VIII heterodimer strongly depends on the presence of von Willebrand Factor, which exhibits a strong affinity to Factor VIII (yet not to Factor VIIIa) and serves as a carrier protein (J. E. Sadler and E. W. Davie: Hemophilia A, Hemophilia B and von Willebrand's disease, in G. Stamatoynnopoulos et al. (Eds.): The molecular basis of blood diseases. W.B. Saunders Co., Philadelphia, 1987, pp. 576-602). It is known that patients suffering from von Willebrand's disease type 3, who do not have a detectable von Willebrand Factor in their blood circulation, also suffer from a secondary Factor VIII deficiency. In addition, the half-life of intravenously administered Factor VIII in those patients is 2 to 4 hours, which is considerably shorter than the 10 to 30 hours observed in Hemophilia A patients. From these findings results that Factor VIII tends to a rapid clearance from the blood circulation and that this process is to some extent inhibited by complexation with its natural carrier, von Willebrand Factor.
Von Willebrand factor (vWF) is a glycoprotein circulating in plasma as a series of multimers typically ranging in size from about 500 to 20,000 kD (or 2 to 40 dimers of vWF). Dimers and multimeric forms of vWF are composed of 250 kD polypeptide subunits linked together by disulfide bonds. vWF mediates the initial platelet adhesion to the sub-endothelium of the damaged vessel wall; only the larger multimers also exhibiting hemostatic activity. Multimerized VWF binds to the platelet surface glycoprotein Gp1bα, through an interaction in the A1 domain of VWF, in order to facilitate platelet adhesion. It is assumed that endothelial cells secret large polymeric forms of vWF and that those forms of vWF which have a low molecular weight (low molecular weight vWF) have arisen from proteolytic cleavage. The multimers having large molecular masses are stored in the Weibel-Palade bodies of the endothelial cells and liberated upon stimulation.
Reduction of FVIII binding activity, due to either reduced vWF protein levels or lowered FVIII binding affinity, results in one of three types of von Willebrand's Disease. In addition to, or alternatively, certain types of von Willebrand's disease are characterized by an increase or decrease in the level of Gp1bα-mediated platelet association, namely in Types 2A, 2B, and 2M (summarized in Castaman et al., Disorders of Hemostasis 88(1):94-108 (2003)). As such, the modulation of vWF interactions with both FVIII and Gp1bα is a viable strategy for the treatment of both Haemophilia and von Willebrand's Disease.
Given the biological importance of vWF, there is a constant need in the art to improve ways for producing vWF for therapeutic applications. It is well known that vWF can be isolated from endogenous sources, such as human blood plasma. The isolated vWF is advantageous in that it has a high specific activity for carrying out its biological function and can, therefore, be used effectively as a therapeutic protein for treating related diseases, such as von Willebrand's disease. Typically, plasma vWF has a specific Ristocetin activity of about 100 mU/μg, but isolation from human blood plasma has disadvantages because, for example, the plasma can contain a variety of viruses, such as HIV and/or hepatitis viruses, which can be transferred to the patient. Furthermore, plasma is a limited resource and, thus, shortages of plasma can be problematic in providing enough vWF for treatment. As such, recombinant methods for producing vWF are advantageous in addressing some of the problems associated with relying on plasma as a source for vWF. For recombinant production, the full length of cDNA of vWF was cloned; the propolypeptide corresponds to amino acid residues 23 to 764 of the full length prepro-vWF (Eikenboom et al (1995) Haemophilia 1, 77 90).
Unfortunately, vWF is a molecule with complex post-translational modifications. Also, the multimerization of the vWF dimers to large and ultralarge multimers in the Golgi apparatus is a challenge for expression in mammalian cells. For example, high molecular weight vWF expressed in cell culture of, e.g., human (primary) endothelial cells depends on the specific storage of ultralarge vWF molecules in Weibel-Palade bodies. Such cell cultures are not suitable for the production of therapeutic proteins. Other cell culture methods have been reported, and it is known that cell culture conditions can affect the production of vWF in a variety of ways. For instance, high concentrations of ammonium (NH4+) have been shown to disturb posttranslational modifications. Mayadas et al. (J. Biol. Chem., 264(23):13497-13503, 1989) demonstrated that levels of 25 mM ammonium resulted in reduced vWF multimerization in endothethial cells, which also negatively affects the specific Ristocetin activity of recombinant vWF. Reduction of multimerization is generally associated in reduction of activity, particularly specific Ristocetin activity, of recombinant vWF.
It still remains difficult to predict which parameters can positively or negatively affect production of a particular protein, especially complex glycoproteins like Factor VIII and vWF. For example, certain components of a cell culture medium have been shown to affect production of Factor VIII. As disclosed in U.S. Pat. No. 5,804,420, the addition of polyol, copper, and other trace metals can positively affect production yield of Factor VIII. As also described in WO 2009/086309, cell culture processes using copper in have been shown to improve production of Factor VIII. Expression of vWF in recombinant CHO cells has also been reported by Mignot et al. (1989). However, none of these examples provide information regarding the specific activity of vWF or its multimeric distribution.
The ADAMTS (a disintegrin and metalloproteinase with thrombospondin type I motifs) proteins are a family of metalloproteinases containing a number of conserved domains, including a zinc-dependant catalytic domain, a cystein-rich domain, a disintegrin-like domain, and at least one, and in most cases multiple, thrombospondin type I repeats (for review, see Nicholson et al., BMC Evol Biol. 2005 Feb. 4; 5(1):11). These proteins, which are evolutionarily related to the ADAM and MMP families of metalloproteinases (Jones G C, Curr Pharm Biotechnol. 2006 February; 7(1):25-31), are secreted enzymes that have been linked to a number of diseases and conditions including thrombotic thrombocytopenic purpura (TTP) (Moake J L, Semin Hematol. 2004 January; 41(1):4-14), connective tissue disorders, cancers, inflammation (Nicholson et al.), and severe plasmodium falciparum malaria (Larkin et al., PLoS Pathog. 2009 March; 5(3):e1000349). Because of these associations, the ADAMTS enzymes have been recognized as potential therapeutic targets for a number of pathologies (Jones G C, Curr Pharm Biotechnol. 2006 February; 7(1):25-31). Accordingly, methods of producing large yields of ADAMTS proteins having high specific activities, which are free of contaminants such as viruses, BSE, and pathogens like Mycoplasma bacteria, are needed.
One ADAMTS family member, ADAMTS13, cleaves von Willebrand factor (vWF) between residues Tyr 1605 and Met 1606, a function responsible for the degradation of large vWF multimers in vivo. Loss of ADAMTS13 activity has been linked to a number of conditions, such as TTP (Moake J L, Semin Hematol. 2004 January; 41(1):4-14), acute and chronic inflammation (Chauhan et al., J Exp Med. 2008 Sep. 1; 205(9):2065-74), and most recently, severe plasmodium falciparum malaria (Larkin et al., PLoS Pathog. 2009 March; 5(3):e1000349).
The ADAMTS13 protease is a 190 kDa glycosylated protein produced predominantly by the liver (Levy et al., Nature. 2001; 413:488-494; Fujikawa et al., Blood. 2001; 98:1662-1666; Zheng et al., J Biol Chem. 2001; 276:41059-41063; Soejima et al., J Biochem (Tokyo). 2001; 130:475-480; and Gerritsen et al., Blood. 2001; 98:1654-1661). Much like the higher order rVWF multimers, recombinant expression of the large ADAMTS13 in mammalian cell culture presents many challenges.
Therefore, there is a need to provide cell culture conditions, particularly large-scale manufacturing culture conditions, that provide consistent total protein yield and/or consistent total and specific activity of the proteins produced between different cell cultures. Consistency among cultures in large-scale manufacturing processes is of importance in the manufacture of therapeutic proteins. There is also a need for cell culture conditions for large-scale production of rVWF with a multimeric distribution and specific Ristocetin activity comparable or higher than VWF as it is present in normal human plasma. Similarly, as ADAMTS proteins have been implicated in a number of diseases and conditions, there is a need in the art for methods of large scale production of recombinant ADAMTS proteins having high specific activities, which are suitable for pharmaceutical formulation and administration. The present invention satisfies these and other needs in the art for the production of recombinant Von Willebrand Factor and recombinant ADAMTS13.